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The Zodiac Killer Code Cracked

The code used by the Zodiac Killer
Is the Zodiac Killer about to be unmasked after all these decades?

In what might be the most important moment in cryptography for decades, a mysterious cipher left by the infamous Zodiac Killer seems to have finally been cracked. Documentary series The Zodiac Killer: Case Closed? has been following an intrepid team of detectives and code-breakers as they’ve delved into this notorious cold case, and it looks like they’ve had their biggest breakthrough yet.

The Zodiac Killer shot and stabbed his way through California in the late 1960s, somehow evading capture despite his habit of taunting the police and media with a string of enigmatic letters and ciphers. The first of these coded messages was cracked very quickly, but the second – known as the Z340 cipher – has beguiled some of the world’s greatest minds since it was sent in 1969.

In the Zodiac Killer: Case Closed?, ace detectives Sal LaBarbera and Ken Mains have been out in the field, following new leads, uncovering new evidence and potentially unidentified Zodiac victims, while back in HQ an elite team of cipher buffs have been trying to decipher the many riddles left by the faceless serial killer – including the Z340. This frighteningly talented group is led by Kevin Knight, a professor of computer science who specialises in machine translation, automata theory and – crucially – decipherment.

The team also includes David Oranchak, another computer whiz and cipher expert, and Sujith Ravi, a research scientist at Google who is adept at using computers to crack codes. There’s Craig Bauer, a professor of mathematics and author of Secret History: The Story of Cryptology. Not to mention Carmel, a super-computer that has been ingeniously programmed to “think” like the Zodiac Killer.

This is no easy thing, because part of the problem with the Zodiac Killer is assessing his level of conscious intent and “talent”. As cold case expert Ken Mains puts it in the series, “He was either the luckiest guy on the face of the Earth, or he was one of the smartest.” Sifting through the clues and communications means asking how much of it is meaningful and how much of it is random, misleading gibberish left by a chaotic mind. Has the Z340 cipher, which is made up of neat grid of esoteric symbols, proved hard to crack because it’s a work of code-making genius, or because it’s a nonsensical mash-up of methodologies, with no overall system that can be deciphered?

This is the question raised by a new discovery by detectives Sal and Ken. Accessing FBI files into the Zodiac, they’ve found a letter that was sent by the President of the American Cryptogram Association, a loose network of hobbyists who enjoy setting and cracking codes. The letter pondered the possibility that the Zodiac was a member of the organisation, which would suggest the killer is/was a civilian rather than a military man. And this would have big implications for the Z340 cipher.

As Kevin Knight explains, “When we're looking at the military angle, we're looking at codes and ciphers that are very well structured, following rigid sets of rules, more like classical music. On the civilian side it's more like jazz, where he's just improvising.”

That would make the code far, far more difficult to crack, and perhaps explains why legions of codebreakers, from talented amateurs to top-level experts, have failed to defeat the Zodiac. But now, in Zodiac Killer: Case Closed?, Craig Bauer looks to have done just that, taking the huge deductive leap many thought wasn’t possible. According to Bauer, the culprit is indeed a civilian, and the Z340 does contain a name.

Is the Zodiac Killer about to be unmasked after all these decades?